Radiation-protecting agent

Abstract

The present invention provides a radiation-protecting agent which protects the active ingredient of radiopharmaceuticals against the radiolysis caused by a reaction of the active ingredient with water radicals formed by radiolysis of water, without decomposing the reactive active ingredient such as readily reducible active ingredient. The radiation-protecting agent of the present invention is characterized by comprising an organic compound usable in medical drugs and having high physiological acceptability and protecting the radiolabeled active ingredient of radiopharmaceuticals against the action of radiation. The reaction rate constant of said organic compound with OH radical, H radical or hydrated electron must be in the range of from 1x108 to 5x1010 M-1s-1, and when added to radiopharmaceuticals, molar concentration of the organic compound must be at least 50 times as high as molar concentration of the active ingredient.

What is claimed is: 
     
       1. A radiopharmaceutical containing a reducible radiolabeled active ingredient and a radiation-protecting agent which comprises an organic compound having high physiological acceptability and being usable in medical drugs and having reactivity with water radicals selected from the group consisting of a OH radical, a H radical and a hydrated electron in a range of from 1×10 8  M -1  s -1  to 5×10 10  M -1  s -1 , wherein said compound protects said reducible radiolabeled active ingredient in the radiopharmaceutical against the action of radiation. 
     
     
       2. A radiopharmaceutical according to claim 1, wherein said organic compound having high physiological acceptability is not reactive with said reducible radiolabeled active ingredient in the radiopharmaceutical. 
     
     
       3. A radiopharmaceutical according to claim 1, wherein said organic compound having high physiological acceptability is a monosaccharide, or a disaccharide, or an organic acid or a salt thereof or an ester thereof. 
     
     
       4. A radiopharmaceutical according to claim 1, wherein said organic compound having high physiological acceptability comprises at least one member selected from the group consisting of glucose, fructose, mannose, galactose, sucrose, maltose, lactose, arabinose, sorbitol, meglumin, sialic acid, lactic acid and benzoic acid or a salt thereof or an ester thereof. 
     
     
       5. A radiodiagnostic agent which contains a radiopharmaceutical according to claims 1, 2, 3 or 4, providing that molar concentration of the radiation-protecting agent is at least 50 times as high as the molar concentration of the active ingredient. 
     
     
       6. A radiotherapeutic agent which contains a radiopharmaceutical according to claims 1, 2, 3 or 4, provided that molar concentration of the radiation-protecting agent is at least 50 times as high as the molar concentration of the active ingredient. 
     
     
       7. A radiodiagnostic agent according to claim 5, wherein said radioisotope is any one member selected from the group consisting of Tc-99m, I-123, I-131, Ga-67, In-111, C-11, N-13, O-15, F-18, Ga-68, Cu-62 and Rb-87. 
     
     
       8. A radiotherapeutic agent according to claim 6, wherein said radioisotope is any one member selected from the group consisting of Y-90, I-131, Sm-153, Dy-165, Ho-166, Lu-177, Re-186, Re-188, At-211 and Cu-67. 
     
     
       9. A method of protecting a reducible radiolabeled active ingredient in a radiodiagnostic agent or a radiotherapeutic agent with a radiation-protecting agent comprising: radiolabeling the active ingredient of the radiodiagnostic agent with a radioisotope selected from the group consisting of Tc-99m, I-123, I-131, Ga-67, In-111, C-11, N-13, O-15, F-18, Ga-68, Cu-62 and Rb-87, or radiolabeling the active ingredient of the radiotherapeutic agent with a radioisotope selected from the group consisting of Y-90, I-131, Sm-153, Dy-165, Ho-166, Lu-177, Re-186, Re-188, At-211 and Cu-67, and adding to the radiodiagnostic agent or radiotherapeutic agent a radiation-protecting agent to protect said reducible radiolabeled active ingredient against the action of radiation, said radiation protecting agent comprising an organic compound reacting with water radicals, selected from the group consisting of a OH radical, a H radical and a hydrated electron in a range of from 1×10 8  M -1  s -1  to 5×10 10  M -1  s -1  wherein the molar concentration of said radiation-protecting agent is at least 50 times as high as the molar concentration of the active ingredient of said radiodiagnostic agent or radiotherapeutic agent.